This disclosure relates to novel aqueous ink-jet inks containing an aqueous vehicle, a pigment and a random polyurethane copolymer as a binder.
Polyurethanes are typically products of the reaction of a polyisocyanate and a polyol. Hard segments are typically made by inclusion of a short chain diol or diamine which when reacted with isocyanates produces urea or carbamate groups within a short distance from each other. The close proximity of urea or carbamate groups is important when intermolecular H-bonding is desired. The intermolecular H-bonding results in the formation of semi-crystalline regions within the polymer matrix. The semi-crystalline regions can be viewed as intermolecular crosslinks that give polyurethanes and polyureas their toughness and elasticity. U.S. Pat. No. 5,128,434 discloses the control of hard segment size in polyurethane formation by reacting two mole equivalents of a diisocyanate with about one mole equivalent of a low molecular weight diol.
A need exists for highly stable and higher-quality inks for ink-jet applications. Although improvements in polyurethane dispersants and binders have significantly contributed to improved ink-jet inks, the current dispersants and binders still do not provide inks with the requisite stability, print nozzle health and lifetime needed for ink-jet applications. The properties of the printed ink such as durability, fastness and optical density (OD) still require improvements. The present invention satisfies this need by providing ink compositions based on a random polyurethane copolymer composition having short hard segments without any ionic group.